section name header

Basics ⬇

Outline

BASICS

Definition!!navigator!!

The equine neonatal eye has many features of immaturity that over time resolve to yield a healthy adult eye. A newborn foal may exhibit lagophthalmos, low tear production, a rounded pupil, reduced corneal sensitivity, lack of a menace response for several weeks, a gray coloration to the iris, hyaloid artery remnants possibly containing blood for hours after birth, prominent lens Y sutures, and a round optic disc with smooth margins. Additionally, neonates commonly have mild ventronasal strabismus that resolves with age.

Pathophysiology!!navigator!!

Congenital, developmental, inherited, and acquired diseases have been identified.

Systems Affected!!navigator!!

  • Ophthalmic
  • Others, if ocular disease is a manifestation of systemic disease

Genetics!!navigator!!

  • Appaloosas, Paso Finos—congenital stationary night blindness (autosomal recessive)
  • Morgan horses, Thoroughbreds—congenital nuclear cataracts (autosomal dominant)
  • Rocky Mountain horses, miniature horses, Mountain Pleasure horses, and Kentucky Saddle horses—multiple congenital ocular anomalies syndrome (semidominant)
  • Belgian draft horse, Thoroughbred, Quarter Horse—aniridia or iris hypoplasia with cataract ± dermoid (suspect autosomal dominant)
  • Quarter Horses—suspected to have a form of inherited optic nerve coloboma

Incidence/Prevalence!!navigator!!

  • Microphthalmos—incidence of 7–14.7%
  • Esotropia in mules—incidence of 0.5%

Signalment!!navigator!!

Equine neonates.

Breed Predilections

  • See Genetics
  • Microphthalmos with cataract and entropion is more common in Thoroughbreds
  • Superficial, irregular corneal epithelial opacities may be found in the eye(s) of Thoroughbred foals. These do not appear painful and resolve with age
  • Congenital glaucoma is seen with more frequency in Thoroughbreds and Standardbreds

Signs!!navigator!!

Dependent on the condition. Ocular discomfort (e.g. blepharospasm, epiphora) and abnormal vision are often observed.

Historical Findings

  • The neonatal foal may have serious, life-threatening problems and can concurrently develop traumatic or inflammatory (peri)ocular disease
  • Alternatively, the neonate may not be adjusting well, gazing off into space with little physical activity, or may be easily startled with reluctance to move. NMS should be a consideration
  • The owner or trainer may notice an abnormal appearance to 1 or both eyes with or without visual or behavioral problems

Physical Examination Findings

  • It is helpful to have people present to handle the mare and assist with restraint of the foal. Sedating a fractious foal can facilitate examination
  • See chapter Ocular examination for a detailed description of the ophthalmic examination process

Causes!!navigator!!

  • Corneal ulcers
    • Trauma
    • Entropion
    • Lagophthalmos
    • Distichia or ectopic cilia (rare)
  • Uveitis
    • Ulcerative keratitis
    • Sepsis, from immune-mediated causes or from Rhodococcus equi, Escherichia coli, Streptococcus equi ssp. equi, Actinobacillus equuli, adenovirus, and EVA
  • Conjunctivitis and subconjunctival hemorrhage
    • Environmental irritants
    • Secondary to pneumonia caused by adenovirus, equine herpesvirus 1, EVA, influenza virus, S. equi ssp. equi, R. equi, and Actinobacillus spp.
    • Trauma during birth
    • NMS
  • Glaucoma
    • Goniodysgenesis
    • Trauma
  • Microphthalmos
    • Congenital
  • Strabismus
    • Congenital
    • Post trauma
  • Blepharitis
    • Fly strike
    • Dermatophytosis
    • Dermatophilus
    • Staphylococcal folliculitis
    • Trauma
  • Entropion
    • Microphthalmia
    • Dehydration
    • Malnutrition
    • Prematurity/dysmaturity
    • Eyelid trauma
    • Cicatrices
  • Dermoids
    • Congenital
  • Nasolacrimal system atresia
    • Congenital
  • Dacryocystitis
    • Nasolacrimal system atresia
    • Systemic illness
  • Aniridia, iridal hypoplasia, enlarged corpora nigra, iridal colobomata
    • Congenital
  • Persistent pupillary membranes
    • Congenital
  • Lens luxation
    • Congenital
    • Post trauma
  • Cataracts
    • Congenital
    • Uveitis
    • Penetrating trauma
  • Retinal dysplasia
    • In utero inflammation
  • Retinal hemorrhage
    • Birthing trauma
  • Retinal detachments
    • Congenital
    • Inflammatory
    • Traumatic
  • Chorioretinitis
    • Possibly maternal systemic disease
  • Optic nerve head colobomas
    • Congenital
  • Optic nerve hypoplasia and optic nerve atrophy
    • Congenital/developmental
    • Inflammation in utero

Risk Factors!!navigator!!

  • “Downer” foals may develop entropion, blepharitis, conjunctivitis, and corneal ulcers
  • Risk factors include malnourishment, sepsis, contact with soiled shavings, and pressure and friction placed on the eyes/eyelids from recumbency
  • Protection of the eyes in these neonates (padding, eye lubricant) is critical

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

N/A

CBC/Biochemistry/Urinalysis!!navigator!!

Usually normal in primary eye disorders.

Other Laboratory Tests!!navigator!!

Cytology and microbial (bacterial and fungal) culture of infected tissue, especially melting corneas or purulent ocular or nasolacrimal discharge.

Imaging!!navigator!!

Dacryocystorhinography to identify nasolacrimal system atresia.

Other Diagnostic Procedures!!navigator!!

  • Complete ophthalmic examination
  • Fluorescein stain, corneal culture and cytology, and Schirmer tear test
  • Topical anesthesia should be applied before corneal cytology is obtained
  • Diagnostic tests for cataract surgery candidates include ocular ultrasonography, electroretinography, and chest radiographs

Pathologic Findings!!navigator!!

Septic ulcerative keratitis will yield a suppurative inflammation with or without bacterial or fungal organisms.

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Aggressive therapy is necessary to preserve vision and eliminate pain in cases of severe uveitis and corneal ulceration. Initially hourly or bihourly instillation of medication is required; subpalpebral lavage placement facilitates this. Lavage placement in the lower fornix is beneficial in nursing foals. These eyes need to be examined several times daily until the clinical signs improve
  • Most other types of neonatal problems can be managed on an outpatient basis

Nursing Care!!navigator!!

  • A “downer” foal with eye disease needs appropriate medical management, and may benefit from a protective eye hood and artificial tear ophthalmic ointment applied 4–6 times daily
  • All hospitalized foals should be monitored daily for corneal ulceration

Activity!!navigator!!

In general, activity is restricted until the ocular lesions are healed.

Diet!!navigator!!

Good nutrition is essential for growth, wound healing, and recuperation.

Client Education!!navigator!!

  • Depending on the severity of disease, hospitalization may be necessary to initiate aggressive therapy. Treatment can be over days to weeks, and surgery may be necessary to preserve vision
  • Neonatal anesthesia of a sick foal is a high-risk event and must be weighed heavily against the benefits of surgery, especially if the newborn is debilitated
  • Genetic information should be shared with clients as necessary

Surgical Considerations!!navigator!!

  • General anesthesia in the neonate is not without risk
  • Conjunctival or amniotic membrane grafting is a common surgery to aid in the healing of severe corneal ulcers
  • Magnification and proper ophthalmic instrumentation is essential to a successful outcome
  • Corneal scarring is a sequela to surgery but may diminish as the foal matures
  • Entropion is corrected by placing temporary vertical mattress sutures in the skin, 2–3 mm from the edge of the eyelid margin. These sutures remain in place until the cause of the entropion is gone. Hotz–Celsus procedures should not be done on neonatal eyelids; the foal usually outgrows neonatal entropion
  • Cataract surgery (phacofragmentation) is performed in foals if no other ocular pathology (e.g. retinal detachment) is discovered during the diagnostic workup
  • Glaucoma can be surgically treated with valve implants or laser surgery when refractive to medical therapy
  • Eyelid lacerations should be corrected with maximal preservation of eyelid tissue. A 2-layer closure of skin–orbicularis muscle and tarsal–conjunctival layers is recommended
  • Keratectomy or blepharoplasty is indicated in the diagnosis and treatment of dermoids
  • Restoration of atretic nasal or palpebral puncta is done by cannulating and flushing the duct through 1 opening, and, after creating a new opening at the other end, leaving the polyethylene or silicone tubing in the duct for several weeks to allow epithelialization of the new puncta and resolution of dacryocystitis
  • Anterior lens luxation requires lens removal to prevent secondary glaucoma
  • Persistent corneal ulcers in foals may need repeated debridement with topical anesthesia and a sterile cotton swab in addition to medical therapy

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Drugs for ulcerative keratitis, uveitis, and glaucoma have been thoroughly outlined in other chapters
  • Intracameral tissue plasminogen activator may be useful in dissolving fibrin clots that develop in the anterior chamber with uveitis

Contraindications!!navigator!!

Topical steroids must not be used on eyes with ulcerative keratitis.

Precautions!!navigator!!

  • Foals on topical atropine should be carefully watched for signs of colic
  • Topical corticosteroids to reduce scarring on a cornea with prior infectious ulcerative keratitis may cause a relapse of the infection

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Rechecks are advised until the eye shows no sign of active disease. If infection or inflammation recurs, a thorough workup is recommended
  • Disease recurrence may also be due to failure to correct the underlying cause (e.g. entropion-induced ulcers)

Prevention/Avoidance!!navigator!!

  • A clean, well-ventilated stall will help prevent infectious or traumatic ocular problems
  • Some congenital lesions such as retinal dysplasia may be less likely if the mare maintains good health during pregnancy

Possible Complications!!navigator!!

Many ocular conditions can impair vision, even when successfully treated.

Expected Course and Prognosis!!navigator!!

  • Most vision-threatening problems in the neonate can be successfully managed if treated accurately and promptly
  • Aphakic foals who had cataracts removed will adjust to their environment but will remain permanently hyperopic
  • Even with complete recovery from an inflammatory disease in the eye, the owner needs to be observant for and report any recurrence of ocular pain

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Sepsis
  • Pneumonia

Age-Related Factors!!navigator!!

N/A

Synonyms!!navigator!!

N/A

Abbreviations!!navigator!!

  • EVA = equine viral arteritis
  • NMS = neonatal maladjustment syndrome

Suggested Reading ⬆ ⬇

Brooks DE. Ophthalmology for the Equine Practitioner, 2e. Jackson, WY: Teton NewMedia, 2008.

Gilger BC. Equine ophthalmology. In: Gelatt KN, Gilger BC, Kern TJ, eds. Veterinary Ophthalmology, 5e. Ames, IA: Wiley Blackwell, 2013:1560–1609.

Gilger BC, ed. Equine Ophthalmology, 3e. Ames, IA: Wiley Blackwell, 2017.

Author(s) ⬆

Author: Shari M. Greenberg

Consulting Editor: Caryn E. Plummer

Acknowledgment: The author and editor acknowledge the prior contribution of Dennis E. Brooks.